1. Field of the Invention
The present invention relates to a method of synthesizing blank and doped hydrophobic silica particles and the use of these particles in, for example, fingerprinting and other applications.
2. Background Information
The development of latent fingerprints generally involves either the use of a dusting agent that adheres to the “sticky” material deposited on the surface following contact, or a chemical developer that produces a visual coloration due to chemical interaction of the applied developer with chemicals commonly found within the deposited materials on the surface, as described in, for example, Champod, C., Lennard, C., Margot, P. and Stoilovic, M., in Fingerprints and Other Ridge Skin Impressions, CRC Press, Boca Raton, 2004 (ISBN 0-415-27175-4) (hereinafter, the “Champod et al. reference”). The size and shape of the powder particles have a large influence on the amount of adhesion they have to the fingerprint, and fine particles tend to adhere better than larger particles, thus resulting in most particles being based on particle sizes of 1-10M, as described in, for example, G. S. Sodhi and J. Kaur, “Powder Method for Detecting Latent Fingerprints: A Review,” Forensic Sci. Int., 120 (2001), pages 172-176 (hereinafter, the “Sodhi et al. reference”). A range of dusting agents are commercially available that are based on a variety of particles, both naturally occurring and synthetic, that show affinity for the hydrophobic materials within the deposited print.
With recent innovations in nanotechnology, potential alternative approaches have been studied. Cadmium sulphide and Europium (III) oxide based powders have been used to visualize latent fingerprints, as described in, for example: E. R. Menzel, S. M Savoy, S. J. Ulvick, K. H. Cheng, R. H. Murdock and M. R. Sudduth, “Photoluminescent Semiconductor Nanocrystals for Fingerprint Detection,” Journal of Forensic Sciences (1999), pages 545-551 (hereinafter, the “first Menzel et al. reference”); E. R. Menzel, M. Takatsu, R. H. Murdock, K. Bouldin and K. H. Cheng, “Photoluminescent CdS/Dendrimer Nanocomposites for Fingerprint Detection,” Journal of Forensic Sciences (2000), pages 770-773 (hereinafter, the “second Menzel et al. reference”); and E. R. Menzel, “Functionalized Europium Oxide Nanoparticles for Fingerprint Detection—A Preliminary Study,” J. Forensic Ident. (hereinafter, the “Menzel reference”). However, these methods are complex and require specialist technical development and expensive instruments, and, hence, are unsuitable to be used in situ, for example, at scenes of crime.
Two reports describe the use of combinations of tetraethoxysilane (TEOS) and phenyltriethoxysilane (PTEOS) to produce relatively hydrophobic silica aerogels (see the first Menzel et al. reference) and the corresponding nanoparticles (see the second Menzel et al. reference) for use in bioanalysis and biosensor applications. The former report demonstrated that as the proportion of PTEOS increased, the hydrophobicity of the resulting sol gel also increased, while the latter report used the particles' hydrophobicity to incorporate the hydrophobic dye, rhodamine 6G, into the resulting particles. The nanoparticles were highly fluorescent with the dye being strongly retained within the particles under aqueous conditions. However, these particles are synthesized using a multi-step route.